Proper monitoring of a system should not be overlooked. Typically we want to know how much power is coming into the system from its charging sources and the state of charge of the battery bank at any point in time. A third and equally important value is how much power is being used by the systems loads. Small systems usually monitor state of charge, or battery voltage and possibly incoming amperage. Medium and larger sized systems typically require a measurement of outgoing power as well, so one can keep track and not over discharge the battery bank.
What is a shunt? A shunt is a device used to measure large DC current, typically the current flowing to and from your battery bank. In more detail a shunt is a precision resistor which produces a very accurate voltage drop when current is passed through the unit. This voltage drop is proportional to the amount of amperage flow, therefore by reading the millivoltage one can observe current flow on a properly calibrated meter.
Do you need a shunt? Depending upon the monitor you select, you may! Small meters with low currents may contain their own shunt, usually those less than 30 amps.
Larger and more complex monitors usually require an external shunt. While some units include a shunt, some do not.
Where is a shunt installed? In the main negative conductor from the battery bank. The shunt is placed close to the battery, bank, typically, in the disconnect enclosure for convenience. Since the shunt produces a voltage drop in millivolts we can run this circuit for a good distance with very small conductors. The monitor can be in the battery room or a good distance away.
Sizing? A 1 to 1 shunt produces 1 millivolt drop per 1 amp of current, therefore 100 mv 100 amp shunt would read 100 amps at 100 millivolts. A 10 to 1 shunt such as a 50 mv - 500 amp shunt offers less resistance and drops only 50 mv with 500 amps of current. Select a shunt for the maximum sustained current of which you will draw. This is usually determined by the inverter size.
Instantaneous and Cumulative Information
Common meters report current flow or battery state of charge (voltage) at a single point in time - the present. This type of metering is termed instantaneous. . Devices which report instantaneous information are less complex and less expensive and can give a general idea of what's happening. Several of the Controller/Regulator units we sell combine metering functions for reduced costs. When reading battery voltage one must fully understand the pushing and pulling effects of battery voltage to use this type of monitoring. (See Battery section).
Cumulative type monitors usually include instantaneous information, but go a step further by recording the power over time. With this information, termed amp hours or watt hours, we can see just how much power we generated yesterday or last month, and how much power was consumed, and with much greater accuracy, determine battery state of charge.
Which ever monitor you select, make sure you have a window, so to speak, of the information you require; without it, you are only guessing and guessing is a common killer of batteries.
Many of the monitors listed here are compatible with the our Power Centers.
Lightning presents a potential hazard for systems with exposed conductors and aluminum framing mounted on rooftops or adjacent to a building. Direct and close-in strikes can damage sensitive electronic circuitry through the presence of static charges and electromagnetic fields. These forces can induce voltage surges and may damage the system's wiring and components, particularly if your system is not properly grounded and protected. While no lightning protection system is foolproof, practical counter-measures are available and include a lightning rod at the PV source, adequate system grounding, and surge protection on the incoming DC wires and the secondary AC wiring.
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